1. Field of the Invention
The invention relates generally to a method for knee surgery, and more specifically, to a method for implanting a uni-condylar knee prosthesis.
2. Discussion of the Related Art
It is well known to perform surgery on a knee having arthritis or other bone degenerating diseases and to resurface the articulating junctions with a prosthetic device. One such method is to resurface only the portion of the knee joint that is effected using a uni-condylar knee prosthesis. One such device is shown in U.S. Pat. No. 3,852,830 to Marmor. Marmor teaches a uni-condylar femoral component and tibial component. The femoral component is thin and the bone is prepared using a bur. The tibial component has a generally flat distal surface and a horizontal cut on the tibia that is below the level of the defect. In fact, many other patents demonstrate a uni-condylar reconstruction surgery such as the patents shown in Table 1.
______________________________________ Pat. No. Inventor Issue Date ______________________________________ Des. 245,259 Shen Aug. 2, 1977 3,715,763 Link Feb. 13, 1973 3,774,244 Walker Nov. 27, 1973 3,953,899 Charnley May 4, 1976 3,958,278 Lee May 25, 1976 4,000,525 Klawitter Jan. 4, 1977 4,034,418 Jackson July 12, 1977 4,055,862 Farling Nov. 1, 1977 4,085,466 Goodfellow April 25, 1978 4,309,778 Buechel Jan. 12, 1982 4,355,429 Mittelmeier Oct. 26, 1982 4,728,332 Albrektsson Mar. 1, 1988 4,743,261 Epinette May 10, 1988 4,795,468 Hodorek Jan 3, 1989 4,838,891 Branemark June 3, 1989 4,963,153 Noesberger Oct. 16, 1990 5,037,439 Albrektsson Aug. 6, 1991 5,092,895 Albrektsson Mar. 3, 1992 5,122,144 Bert June 16, 1992 5,171,244 Caspari Dec. 5, 1992 5,171,276 Caspari Dec. 15, 1992 5,201,768 Caspari April 13, 1993 5,207,711 Caspari May 4, 1993 5,228,459 Cas ari July 20, 1993 ______________________________________
The above patents all disclose a flat bone engaging surface and a cut on the tibia that is horizontal.
The patents disclose at least two ways that the tibia is prepared for the implant. The first is to make a horizontal cut starting just off of the midline in either the medial or lateral compartment of the knee, thereby preserving the anterior and posterior ligaments. The cuts vary in that one extends the remaining distance to the outermost portion of the tibia or stops short of cutting away the last portion of the cortical bone and uses the remaining bone to help secure the component from lateral movement. Some uni-condylar components have been reported to subside upon long-term use and subsequently must be revised. If the surgeon does not get the tibial component properly aligned and out to the hard cortical bone, the component may have a tendency to sink into the softer bone in the center region of the tibia plateau.
Other knee designs showing an angle or wedge concept exist such as those shown in the patents in Table 2.
______________________________________ Pat. No. Inventor Issue Date ______________________________________ 4,178,641 Grundei Dec. 18, 1979 5,019,103 Van Zile May 28, 1991 5,047,058 Roberts Sept. 10, 1991 5,152,797 Luckman Oct. 6, 1992 5,344,461 Phlipot Sept 6, 1994 5,387,241 Hayes Feb. 7, 1995 5,458,637 Hayes Oct. 7, 1995 5,531,793 Kelman July 2, 1996 5,549,688 Ries Aug. 27, 1996 ______________________________________
The designs shown in the above-reference patents are designed to fill a gap created after making an initial horizontal or posterior sloped cut. The wedges are used to make up a gap that would otherwise have to be filled with bone cement or a lower horizontal cut would need to be made. The wedges are used mostly in revision surgery or in cases with severe bone degeneration that would require a large resection. There is no suggestion to use the wedge concept in a primary uni-condylar device. In fact, the wedge concept is used to make a thicker component.
Assignee of the present invention has previously commercialized a uni-condylar tibial component that uses a wedge shape that follows the slope of the sclerotic bone. The inventor of the present application recognized that an improvement could be made to make locating the tibial component on the tibial plateau easier when cementing on the device.
What is needed then is a method of implanting a uni-condylar knee prosthesis that follows the sclerotic bone that is present in a single compartment diseased knee and is easier to locate.